Capacity control apparatus for compressors

ABSTRACT

An apparatus for controlling compressor discharge capacity includes a variable capacity compressor, a capacity adjustment device, a signal processing device, a capacity setting device, and a signal comparing device. The capacity adjustment device regulates a discharge capacity of the variable capacity compressor. The signal processing device receives a signal corresponding to a discharge capacity of the variable capacity compressor. The capacity setting device sets a first discharge capacity target value for the variable capacity compressor. The signal comparing device compares the discharge capacity signal to the fist discharge capacity target value and sends an activation signal to the capacity adjustment device, such that the discharge capacity signal approaches the first discharge capacity value.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a capacity control apparatusfor variable capacity-type compressors for use in automotive airconditioning systems. In particulars the present invention relates to acapacity control apparatus that may directly control an actual dischargecapacity of variable capacity-type compressors, and which may be used tocontrol refrigeration circuits in automotive air conditioning systems

2. Description of Related Art

A capacity control apparatus for a variable capacity-type compressor isdescribed in, for example, Japanese (Unexamined) Patent Publication No.64-073178. In this known variable capacity-type compressor, a dischargecapacity of the compressor is regulated by a control means, e.g., anelectromagnetic valve or the like. The control means regulates thedischarge capacity of the compressor based on a measured physicalcharacteristic related to cooling efficiency of a refrigeration circuit,e.g., a pressure or a temperature of a refrigerant.

In this known variable capacity-type compressor, the actual dischargecapacity of the compressor may be adjusted, as needed. For example, thedischarge capacity of the compressor may be adjusted in response to acondition of the refrigeration circuit, e.g., to an increased airconditioning load on the refrigeration circuit. Moreover, actualdischarge capacity of the compressor may be adjusted toward apredetermined discharge capacity target of the compressor. For example,a target discharge capacity value of the compressor may be established,and the actual discharge capacity may be adjusted toward the targetdischarge capacity value. Therefore, in such known variable capacitytype compressors, in which an engine of a vehicle may drive thecompressor, a load fluctuation of the compressor may not correspond to aload of the engine. As a result, efficient operation of the compressormay not be achieved.

In order to improve the efficiency of such compressors, such compressorsmay include a discharge capacity control apparatus for a variablecapacity-type compressor, as described in Japanese Patent No. 3060676.In this known variable capacity-type compressor, a torque detectiondevice is positioned on the compressor to measure a torque of a drive ofthe compressor, e.g., a torque of a drive shaft of a compressor or thelike. An output of a vehicle engine then may be adjusted based on themeasured value of torque driving the compressor.

Nevertheless, in known variable capacity-type compressors having such atorque detection device, the compressor load is measured, and thismeasurement is used to control the air conditioning system of thevehicle. Nevertheless, the discharge capacity of the compressor is notadjusted toward a predetermined target discharge value of thecompressor.

SUMMARY OF THE INVENTION

Therefore, a need has arisen for a discharge capacity, control apparatusfor variable capacity-type compressors that regulates operation of thecompressor, so that the compressor discharge capacity approaches orreaches a discharge capacity target value.

According to an embodiment of the present invention, an apparatus forcontrolling compressor discharge capacity comprises a variable capacitycompressor, a capacity adjustment device, a signal processing device, acapacity setting device, and a signal comparing device. The capacityadjustment device regulates a discharge capacity of the variablecapacity compressor. The signal processing device receives a signalcorresponding to a discharge capacity of the variable capacitycompressor. The capacity setting device sets a first discharge capacitytarget value for the variable capacity compressor. The signal comparingdevice compares the discharge capacity signal to the first dischargecapacity target value and second an activation signal to the capacityadjustment device, such that the discharge capacity signal approachesthe first discharge capacity target value.

In another embodiment of the invention, an apparatus for controllingcompressor discharge capacity comprises a variable capacity compressor,a capacity adjustment device, a signal processing device, a capacitysetting device, a first signal comparing device, a detection device apressure setting device, and a second signal comparing device. Thecapacity adjustment device regulates a discharge capacity of thevariable capacity compressor. The signal processing device receives asignal corresponding to a discharge capacity of said variable capacitycompressor. The capacity setting device sets a first discharge capacitytarget value of the variable capacity compressor. The first signalcomparing device compares the discharge capacity signal to the firstdischarge capacity target value and sends a first activation signal tothe capacity adjustment device, such that the discharge capacity signalreaches the first discharge capacity value. The detection device detectsa first pressure value in a refrigeration circuit including the variablecapacity compressor. A pressure setting device sets a second pressuretarget value. A second signal comparing device compares the firstpressure value with the second pressure target value and sends anactivation signal to the capacity adjustment device, such that the firstpressure value approaches the second pressure target value. Thecompressor discharge capacity controlling apparatus may comprise aswitching device that selectively connects the first signal comparingdevice and the second signal comparing device to the capacity adjustmentdevice.

In another embodiment of the invention, an apparatus for controllingcompressor discharge capacity comprises a variable capacity compressor,a capacity adjustment device, a signal processing device, a capacitysetting device, a first signal comparing device, a detection device, atemperature setting device, and a second signal comparing device. Thecapacity adjustment device regulates a discharge capacity of thevariable capacity compressor. The signal processing device receives asignal corresponding to a discharge capacity of said variable capacitycompressor. The capacity setting device sets a first discharge capacitytarget value of the variable capacity compressor. The first signalcomparing device compares the discharge capacity signal to the firstdischarge capacity target value and sends an activation signal to thecapacity adjustment device, such that the discharge capacity signalreaches the first discharge capacity value. The detection device detectsa first temperature value in a refrigeration circuit including thevariable capacity compressor. A temperature setting device sets a secondtemperature target value. A second signal comparing device compares thefirst temperature value with the second temperature target value andsends an activation signal to the capacity adjustment device, such thatthe first temperature value approaches the second temperature targetvalue. The compressor discharge capacity controlling apparatus maycomprise a switching device that selectively connects the first signalcomparing device and the second signal comparing device to the capacityadjustment device.

According to a further embodiment of the invention, a method ofcontrolling a discharge capacity of a variable capacity compressorconnected to a refrigeration circuit comprises the following steps. Afirst discharge capacity value of the variable capacity compressor isset. A discharge capacity of the variable capacity compressor isdetected. The discharge capacity value is compared with the firstdischarge capacity target value. The discharge capacity of the variablecapacity compressor is adjusted, such that the discharge capacity valueapproaches the first discharge capacity value.

Other objects, features, and advantages of embodiments of this inventionwill be apparent to persons of ordinary skill in the art from thefollowing detailed description of the invention and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be understood more readily with reference tothe following drawings.

FIG. 1 shows a schematic of a capacity control apparatus of acompressor, according to an embodiment of the present invention.

FIG. 2 shows a schematic of a capacity control apparatus of acompressor, according to another embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Where features of the following embodiments of the present invention aresubstantially similar to those of other embodiments, similar parts havebeen given similar numbers, and explanations for these similar parts maybe omitted from the descriptions of subsequent embodiments.

FIG. 1 shows a discharge capacity control mechanism 1 of a variablecapacity-type compressor 2 for a vehicle air conditioning systemaccording to an embodiment of the present invention. Variablecapacity-type compressor 2 may be a swash plate-type compressor.Variable capacity-type compressor 2 may comprise a cylinder block 12, afront housing 7, and a cylinder head 14. Cylinder block 12 may besubstantially cylindrical. Front housing 7 may be positioned at one endof cylinder block 12. Cylinder head 14 may be positioned at another endof cylinder block 12. A crank chamber 8 may be formed between cylinderblock 12 and front housing 7. Moreover, a suction chamber 15 and adischarge chamber 16 may be formed within cylinder head 14. Cylinderblock 12, front housing 7, and cylinder head 14 may be connected by aplurality of fasteners, e.g., bolts (not shown). Compressor 2 also maycomprise a plurality of cylinder bores 13 formed in cylinder block 12.Cylinder bores 13 may be positioned around a central axis of cylinderblock 12, e.g., in an annular configuration, and may be offset radiallyfrom the central axis of cylinder block 12.

Compressor 2 may comprise a drive shaft 4, a cam rotor 5, a swash plate6, a plurality of pairs of shoes 10, and a plurality of pistons 11.Drive shaft 4 may extend through crank chamber 8, alone a central axisof compressor 2. Drive shaft 4 may be supported rotatably by fronthousing 7 and cylinder block 12, via bearings 30 a and 30 b, which maybe mounted in front housing 7 and cylinder block 12, respectively.Compressor 2 may comprise an electromagnetic clutch 3. A drive belt (notshown) may engage a pulley of electromagnetic clutch 3 and transmit adriving force from a driving source (not shown), e.g., an engine of avehicle, to electromagnetic clutch 3. When electromagnetic clutch 3engages drive shaft 4, the driving force off the driving source may betransmitted by electromagnetic clutch 3 to drive shaft 4. Moreover, camrotor 5 may be fixed to drive shaft 4 to rotate with drive shaft 4 andmay be positioned within crank chamber 8. Swash plate 6 also may bepositioned within crank chamber 8 and may be slidably mounted on driveshaft 4. Swash plate 6 may be connected to cam rotor 5 via hingemechanism 9, so that an inclination angle of swash plate 6 may vary, andso that swash plate 6 may rotate with drive shaft 4. Althoughelectromagnetic clutch 3 may transmit the driving force of the drivingsource to drive shaft 4, the driving source may be coupled directly todrive shaft 4 in another embodiment of the present invention.

A piston 11 may be positioned within each cylinder bore 13, so that eachpiston 11 may reciprocate independently within its respective cylinderbore 13. Each piston 11 may include a pair of substantiallysemispherical cavities, which may be formed at an end of each piston 11.Each piston 11 may be connected to swash plate 6, via a pair of shoes10. Each shoe 10 comprises a semispherical portion and a flat portion. Asemispherical portion of each shoe may be positioned in a respectivesemispherical cavity of each piston 11, while a flat portion of eachshoe may contact a surface of swash plate 6. In this way, each shoe of apair of shoes 10 may slidably contact a surface of swash plate 6.

Compressor 2 may comprise a discharge capacity adjustment device 17 awhich may adjust a discharge capacity of compressor 2. Capacityadjustment device 17 a may comprise an electromagnetic control valve 17,a first communication path 18, and a second communication path 19. Firstcommunication path 18 and second communication path 19 may establishcommunication between discharge chamber 16 and crank chamber 8.Electromagnetic control valve 17 may be positioned between firstcommunication path 18 and second communication path 19. Electromagneticcontrol valve 17 may be opened to enable fluid communication betweenfirst communication path 18 and second communication path 19 or closedto prevent fluid communication between first communication path 18 andsecond communication path 19. In this way, electromagnetic control valve16 may control the amount of refrigerant that flows between crankchamber 8 and discharge chamber 16.

Capacity adjustment device 17 a may control the discharge capacity ofcompressor 2 in the following manner. The discharge capacity ofcompressor 2 may vary with a length of a stroke of each piston 11. Thelength of a stroke of each piston. 11 may vary with the inclinationangle of swash plate 6. The inclination angle of swash plate 6 may becontrolled by controlling a pressure in crank chamber 8. The pressure incrank chamber 8 may be controlled by controlling the amount of arefrigerant, e.g., a refrigerant gas, that passes between crank chamber8 and discharge chamber 16, via first communication path 18 and secondcommunication path 19. By controlling the amount of refrigerant thatflows between crank chamber 8 and discharge chamber 16 via firstcommunication path 18 and second communication path 19, capacityadjustment device 17 a may control the inclination angle of swash plate6 and the stroke length of each piston 11, thereby enabling capacityadjustment device 17 a to control the discharge capacity of compressor2.

A rod 21 may be positioned within drive shaft 4 and may slide in anaxial direction within drive shaft 4, i.e., in a direction substantiallyparallel to a longitudinal axis of drive shaft 4. Swash plate 6 may beconnected to rod 21, via a pin 20. Rod 21 may slide within drive shaft 4in an axial direction in response to changes in the inclination angle ofswash plate 6. Thus, a position of rod 21 in an axial direction withindrive shaft 4 corresponds to an inclination angle of swash plate 6. Adetection member 22 may be positioned at an end of rod 21 that projectsfrom drive shaft 4. A position sensor 23 a may detect a position ofdetection member 22. Thus, a position of rod 21 and an inclination angleof swash plate 6 may be detected by position sensor 23 a, via detectionof a position of detection member 22. Because the discharge capacity ofcompressor 2 and stroke length of each piston correspond to theinclination angle of swash plate 6, the discharge, capacity ofcompressor 2 may be measured by detecting a position of detection member22. Moreover, the discharge capacity of compressor 2 and the strokelength of each piston 11 may be converted to a position of rod 21, viaswash plate 6 and pin 20, such that a discharge capacity of compressor 2may be derived from a detected position of rod 21. This mechanismconstitutes a capacity detection device 23 according to an embodiment ofthe invention.

A capacity control device 24 may be connected to position sensor 23 a ofcapacity detection device 23 and electromagnetic control valve 17 ofcapacity adjustment device 17 a. Capacity control device 24 may comprisea signal processing device 25, e.g., an electric circuit, a capacitysetting device 26, e.g., an electric circuit, a signal comparing device27, e.g., an electric circuit, and an amplifier 28 for energizing asolenoid of electromagnetic valve 17. Signal processing device 25 mayreceive signals from position sensor. 23 a of capacity detection device23. Each signal may correspond to a position of detection member 22 androd 21 detected by position sensor 23 a of capacity detection device 23and thus to a position of swash plate 6 and to a discharge capacity ofcompressor 2.

Capacity setting device 26 may establish a compressor discharge capacitytarget value. Signal comparing device 27 may compare the detected signalreceived from signal processing device 25 to the compressor dischargecapacity target value. Based on the comparison, signal comparing device21 may transmit a feedback value signal to amplifier 28. Feedback valuesignal may be based on a difference, if any, between the detected signaland the compressor discharge capacity target value. In response to thereceived feedback value signal, amplifier 28 transmits an activationsignal to electromagnetic valve 17 to energize the solenoid ofelectromagnetic control valve 17. Thus, by establishing compressordischarge capacity target values, capacity setting device 26 may controla pressure in crank chamber 8, thereby controlling the dischargecapacity of compressor 2 based on the compressor discharge capacitytarget value. Each compressor discharge capacity target value may beselected from values in a range of about 0% of a discharge capacitytarget value to about 100% of a discharge capacity target

According to this embodiment of the invention, the discharge capacity ofcompressor 2 may be detected directly, i.e., by detecting a position ofrod detection member 22 and rod 21, and by converting that detectedposition to a corresponding discharge capacity of compressor 2. Thisdetected discharge capacity may be compared to a predetermined dischargecapacity target value, so that the discharge capacity of compressor 2may be regulated without regard to other factors that may affect thedischarge capacity of compressor 2. For example, a feedforward controlmay be used to adjust the discharge capacity of compressor 2, so thatthe detected value of a position of rod 21 and, thus, the dischargecapacity of compressor 2 may approach and eventually reach a dischargecapacity target value.

FIG. 2 shows a discharge capacity control mechanism 1′ of a variablecapacity-type compressor 2′ for a vehicle air conditioning systemaccording to a further embodiment of the present invention. In thisembodiment of the invention, the configuration of discharge capacitycontrol mechanism 1′ may be substantially similar to the configurationof discharge capacity control mechanism 1 of the previous embodiment,except that discharge capacity control mechanism 1′ may comprise asecond capacity control device 31. Second capacity control device 31 maycontrol the discharge capacity of compressor 2′ through a feedbackcontrol based on a signal that corresponds to a detected pressure or adetected tempera of a refrigeration circuit. Moreover, dischargecapacity control mechanism 1′ may comprise first capacity control device24′ in addition to second capacity control device 31, so that adischarge capacity of compressor 2 may be regulated by first capacitycontrol device 24′ via a feedback control based on a signal thatcorresponds to a detected position, of rod 21, as discussed in theprevious embodiment, or through a, feedback control based on a signalthat corresponds to a detected pressure or a detected temperature of arefrigeration circuit. According to this embodiment, a switching device37 may connect second capacity control device 31 or first capacitycontrol device 24′ to amplifier 28.

Second capacity control device 31 may comprise a sensor, e.g., apressure sensor 33 a, a temperature sensor 33 b, or the like, a signalprocessing device 34, e.g., an electric circuit, a pressure settingdevice 35, e.g., an electric circuit, a signal comparing device 36,e.g., an electric circuit, and an amplifier 28 for energizing a solenoidof electromagnetic valve 17. Pressure sensor 33 a may be positioned in arefrigeration circuit. For example, pressure sensor 33 a may bepositioned between a suction chamber 15 of compressor 2′ and anevaporator 32 to detect a pressure of refrigerant in the refrigerationcircuit, e.g., a pressure of refrigerant in suction chamber 15 ofcompressor 2′. Pressure setting device 35 may set a pressure controltarget value. Signal comparing device 36 may compare the pressuredetected by pressure sensor 33 a with the predetermined pressure controltarget value set by pressure setting device 35. Based on thiscomparison, signal comparing device 36 may transmit a feedback valuesignal to amplifier 28. The feedback value signal may correspond to adifference, if any, between the pressure detected by pressure sensor, 33a and the predetermined pressure control target value set by pressuresetting device 35. Amplifier 28 may transmit a signal to electromagneticvalve 17 to energize the solenoid of electromagnetic control valve 17.

Thus, the discharge capacity of compressor 2′ may be controlled bydetection a pressure of a refrigerant in a refrigeration circuit and bycomparing the detected pressure to a predetermined pressure controltarget value set by pressure setting device 35. A feedforward control orthe like, may be used to control second capacity control device 31, sothat the detected pressure value approaches and reaches thepredetermined target pressure control value.

In another embodiment of the invention, a temperature sensor 33 b maydetect a temperature of refrigeration circuit, e.g., a temperature offins of evaporator 32, a temperature of air passing through evaporator32, or the like. Pressure setting device 35 may set a temperaturecontrol target value. Signal comparing device 36 may compare thetemperature detected by temperature sensor 33 b with the temperaturecontrol target value set by pressure setting device 35. Based on thiscomparison, signal comparing device 36 may transmit a feedback valuesignal to amplifier 28. The feedback value signal may correspond to adifference, if any, between the temperature detected by temperaturesensor 33 a and the temperature control target value set by pressuresetting device 35. Amplifier 28 may transmit a signal to electromagneticvalve 17 to energize the solenoid of electromagnetic control valve 17.Thus, capacity control device 31 enables regulation of the dischargecapacity of compressor 2′, via the detected temperature of evaporator 32or the detected pressure of refrigerant in the refrigeration circuit.

A switching device 37 may selectively connect first capacity controldevice 24′ and second capacity control device 31 to amplifier 28. Forexample, switching device 37 may connect first capacity control device24′ to amplifier 28, so that signal comparing device 27 may send afeedback signal to capacity adjustment device 17 a. Switching device 37may connect second capacity control device 31 to amplifier 28, so thatsignal comparing device 36 may send a feedback signal to capacityadjustment device 17 a Switching device 37 may be activated by anexternal controller (not shown). External controller may activateswitching device 37 to connect first capacity control device 24′ orsecond capacity control device 31 to amplifier 28 depending upon adesired outcome, e.g., reducing energy consumption, matching a load ofcompressor 2′ to a load of the vehicle engine, controlling the flow ofrefrigerant in the refrigeration circuit, or the like.

Thus, according to one embodiment of the invention, a discharge capacitycontrol device may regulate the discharge capacity of a compressordirectly, e.g., by detecting the discharge capacity of a compressor andregulating the detected discharge capacity toward a predetermineddischarge capacity control value, without regard to other factors thatmay affect the discharge capacity of the compressor. Moreover, accordingto another embodiment of the invention, a discharge capacity controldevice may regulate the discharge capacity of a compressor indirectly,e.g., by detecting a pressure or a temperature of a refrigerationcircuit, so that the detected discharge capacity may be adjusted basedon a variety of considerations, e.g., reducing energy consumption,matching a load of compressor 2′, to a load of the vehicle engine,controlling the flow of refrigerant in the refrigeration circuit, or thelike. In addition, the discharge capacity control device of the presentinvention may regulate discharge capacity by a feedforward control, sothat discharge capacity of the compressor may be regulated in anefficient manner.

While the invention has been described in connection with preferredembodiments, the invention is not limited thereto. It will be understoodby those skilled in the art that other embodiments, variations andmodifications of the invention will be apparent to those of ordinaryskill in the art from a consideration of the specification or a practiceof the invention disclosed herein and may be made within the scope ofthe invention.

What is claimed is:
 1. A method of controlling a discharge capacity of avariable capacity compressor connected to a refrigeration circuit,comprising the steps of: setting a first discharge capacity target valueof said variable capacity compressor; detecting a discharge capacity ofsaid variable capacity compressor and transmitting a discharge capacitysignal corresponding thereto; comparing said discharge capacity signalwith said first discharge capacity target value; and adjusting saiddischarge capacity of said variable capacity compressor, such that saiddischarge capacity value approaches said first discharge capacity,target value.
 2. The method of claim 1, further comprising the steps of:detecting a first pressure value in said refrigeration circuit; settinga second pressure target value; comparing said first pressure value withsaid second pressure target value; adjusting a discharge capacity ofsaid variable capacity compressor, such that said first pressure valueapproaches said second pressure target value.
 3. The method of claim 2,wherein the step of adjusting a discharge capacity of said variablecapacity compressor comprises the steps of: connecting a second signalcomparing, device to a capacity adjustment device; and sending a secondactivation signal to said capacity adjustment device, which adjusts saiddischarge capacity based on said second activation signal, such thatsaid first pressure value approaches said second pressure target value.4. The method of claim 1, further comprising the steps of: detecting afirst temperature value in said refrigeration circuit; setting a secondtemperature target value; comparing said first temperature value withsaid second temperature target value; adjusting a discharge capacity ofsaid variable capacity compressor, such that said first temperaturevalue approaches said second temperature target value.
 5. The method ofclaim 4, wherein the step of adjusting a discharge capacity of saidvariable capacity compressor comprises the steps of: connecting a secondsignal comparing device to a capacity adjustment device; and sending asecond activation signal to said capacity adjustment device, whichadjusts said discharge capacity based on said second activation signal,such that said fist temperature value approaches said second temperaturetarget value.
 6. The method of claim 1, wherein the step of adjusting adischarge capacity of said variable capacity compressor comprises thesteps of: connecting a first signal comparing device to a capacityadjustment device; and sending a first activation signal to saidcapacity adjustment device, which adjusts said discharge capacity basedon said first activation signal, such that said discharge capacity valueapproaches said first discharge capacity target value.
 7. An apparatusfor controlling compressor discharge capacity comprising: a variablecapacity compressor; a capacity adjustment device, which regulates adischarge capacity of said variable capacity compressor; a signalprocessing device, which receives a signal corresponding to a dischargecapacity of said variable capacity compressor; a capacity settingdevice, which sets a first discharge capacity target value for saidvariable capacity compressor; and a signal comparing device, whichcompares said discharge capacity signal to said first discharge capacitytarget value and sends an activation signal to said capacity adjustmentdevice, such that said discharge capacity signal approaches said firstdischarge capacity target value.
 8. The apparatus of claim 7, whereinsaid variable capacity compressor is connected to a refrigerationcircuit of a vehicle air conditioning system.
 9. The apparatus of claim7, wherein said variable capacity compressor is a swash plate-type,variable displacement compressor.
 10. The apparatus of claim 7, furthercomprising: a feedforward control, which controls said signal comparingdevice, such that said discharge signal approaches said first dischargecapacity target value.
 11. An apparatus for controlling compressordischarge capacity comprising: a variable capacity compressor; acapacity adjustment device, which regulates a discharge capacity of saidvariable capacity compressor; a signal processing device, which receivesa signal corresponding to a discharge capacity of said variable capacitycompressor; a capacity setting device, which sets a first dischargecapacity target value of said variable capacity compressor; a firstsignal comparing device, which compares said discharge capacity signalto said first discharge capacity target value and sends a firstactivation signal to said capacity adjustment device, such that saiddischarge capacity signal approaches said first discharge capacityvalue; a detection device, which detects a first pressure value in arefrigeration circuit including said variable capacity compressor; apressure setting device, which sets a second pressure value; a secondsignal comparing device, which compares said first pressure value withsaid second pressure value and sends a second activation signal to saidcapacity adjustment device, such that said first pressure valueapproaches said second pressure value.
 12. The apparatus of claim 11,further comprising: a switching device, which selectively connects saidfirst signal comparing device to said capacity adjustment device, sothat said first signal comparing device sends said first activationsignal to said capacity adjustment device.
 13. The apparatus of claim11, further comprising: a switching device, which selectively connectssaid second signal comparing device to said capacity adjustment device,so that said second signal comparing device sends said second activationsignal to said capacity adjustment device.
 14. The apparatus of claim11, wherein said variable capacity compressor is connected to arefrigeration circuit of a vehicle air conditioning system.
 15. Theapparatus of claim 11, wherein said variable capacity compressor is aswash plate-type, variable displacement compressor.
 16. The apparatus ofclaim 11, further comprising: a feedforward control, which controls saidfist signal comparing device, such that said discharge signal approachessaid first discharge capacity value and which controls said secondsignal comparing device, such that said first pressure value approachessaid second pressure value.
 17. An apparatus for controlling compressordischarge capacity comprising: a variable capacity compressor; acapacity adjustment device, which regulates a discharge capacity of saidvariable capacity compressor; a signal processing device, which receivesa signal corresponding to a discharge capacity of said variable capacitycompressor; a capacity setting device, which sets a first dischargecapacity target value of said variable capacity compressor; a firstsignal comparing device, which compares said discharge capacity signalto said first discharge capacity target value and sends a firstactivation signal to said capacity adjustment device, such that saiddischarge capacity signal approaches said first discharge capacityvalue; a detection device, which detects a first temperature value in arefrigeration circuit including said variable capacity compressor; apressure setting device, which sets a second temperature value; a secondsignal comparing device, which compares said first temperature valuewith said second temperature value and sends a second activation; signalto said capacity adjustment device, such that said first temperaturevalue approaches said second temperature value.
 18. The apparatus ofclaim 17, further comprising: a switching device, which selectivelyconnects said first signal comparing device to said capacity adjustment,device so that said first signal comparing device sends said firstactivation signal to said capacity adjustment device.
 19. The apparatusof claim 17, further comprising: a switching device, which selectivelyconnects said second signal comparing device to said capacity adjustmentdevice, so that said second signal comparing device sends said secondactivation signal to said capacity adjustment device.
 20. The apparatusof claim 17, wherein said variable capacity compressor is connected to arefrigeration circuit of a vehicle air conditioning system.
 21. Theapparatus of claim 17, wherein said variable capacity compressor is aswash plate-type, variable displacement compressor.
 22. The apparatus ofclaim 17, further comprising: a feedforward control, which controls saidfirst signal comparing device, such that said discharge signalapproaches said first discharge capacity value and which controls saidsecond signal comparing device, such that said first temperature valueapproaches said second temperature value.